This invention relates to a thermal ink-transfer printing apparatus capable of recording high-quality pictures.
With the rapid spread of information-communicating means, attention has come to focus on recording apparatuses as terminal equipment. A recording apparatus of the conventional impact printer type has been subject to several drawbacks, such as high recording noise, low printing speed, high cost, etc.
A thermal ink-transfer printing apparatus has come to be considered as a recording apparatus to take the place of the impact printer type. In this thermal ink-transfer printing apparatus, an ink film carrying ink which may be softened or melted by heating is joined with a recording sheet, and heat is applied to a predetermined picture region so that the softened or melted ink is transferred to the recording sheet. The printing apparatus of this type has a simple recording principle and a simple configuration. Moreover, the thermal ink-transfer printing apparatus provides satisfactory recording performance, ensuring good preservation and substantially no falsifiability of recorded pictures and producing hardly any recording noise. In the thermal ink-transfer system, however, heat must be applied instantaneously to the ink film for uniform heating of the picture region. Therefore, the quality of the recorded pictures will be reduced unless the thermal ink transfer is performed with high reliability and with high accuracy.
The inventors hereof have proposed a thermal ink-transfer printing apparatus capable of forming polychrome pictures, as shown in FIG. 1. In this printing apparatus, an ink film 2, which is divided along its feeding direction into several regions individually carrying ink layers of a plurality of colors, is fed in one direction, while a recording sheet 4 is moved in that direction and another direction. A thermal head 6 has a heating resistor array whose length is equal to or shorter than the widths of the ink film 2 and the recording sheet 4. Thermal ink transfer is repeated for the individual colors to form a polychrome picture on the recording sheet 4. In this case, the ink film 2 is required to quickly transmit the heat from the heating resistor array of the thermal head 6 to the ink of the ink film 2. Accordingly, the ink film 2 is made extremely thin and so lacks firmness. Moreover, the width of the ink film 2 is quite large, depending on the width of the transfer region. Accordingly, the ink film 2 will readily be wrinkled unless it is fed with high accuracy and in a well-balanced manner. When the wrinkled ink film 2 is clamped between the thermal head 6 and the recording sheet 4, the wrinkles will build up into a fold unless the wrinkles are removed before the film 2 reaches the head 6. As a result, the conditions of thermal transmission will fluctuate to cause defective ink transfer, such as transfer slip, as it is sometimes called. Thus, the quality of recorded pictures will be deteriorated. Although the method of winding the ink film 2 was improved for uniform transverse winding, it proved impossible to prevent the ink film 2 from being wrinkled.